The invention described in this document provides the system concept of a multi-tiered integrated wireless access network. The innovation includes the design of each tier to “fit seamlessly” in the multi-tiered architecture. In comparison, previous-disclosed networks typically consist of one tier only, which neither provide scalability nor are designed with lower or higher wireless network tiers in mind.
Fitting seamlessly, as mentioned above, is defined in terms of connectivity and interference avoidance. Within the described network, each tier operates in a different frequency band, hence achieving total interference avoidance, but prohibiting interoperability.
For network tiers outside the scope of this invention, which may be attached on top or below the described network for example WLAN (Wireless Local Area Networks) or PAN (Personal Access Networks), and which may operate within the same frequency band, CCA (Carrier Controlled Access) will be employed to allow for graceful coexistence. Devices meant for operation in the Ad-hoc Mesh Tier will be capable of interoperability with WLAN's. That is, these devices will be able to switch operation from one tier into the other.
Connectivity in the above sense is defined as the possibility to connect co-located devices from different tiers back to back. Interoperability is defined as the capability of a device made to function in one tier in a certain mode and to function in another tier in that same mode.
The notion of a multi-tiered architecture is relevant due to the fact that it provides flexible and scalable network deployment, which provides high cost efficiency especially in the mesh architecture of the lowest tier. Thus, increasing the throughput can easily be achieved by inserting only a new node into the tier above, without manual reconfiguration of any other devices. This compared to a one-tier approach, where increasing bandwidth demand often can only be met by a total reconfiguration of the whole (sub)-network.
This flexibility and scalability allows the network operator the unique ability to start the network small, extending it as demand increases, whereas other networks generally need to be fully pre-deployed (wired networks), or pre-deployed to a large extent to avoid the huge cost of network extension (one-tier wireless approaches).
The notion of a multi-tiered architecture is also relevant due to the fact that it avoids the trade-off between technology cost and performance demands. For a one-tiered network, for example a network in the LMDS band, the throughput can be made adequate throughout the network, but the cost of a CPE is high due to the high cost of RF-technology in this band. For a one-tiered network in the 2.4 GHz band for example, the CPE cost is comparatively much lower, however, the achievable throughput, with current state of the art technology, is lacking. The multi-tiered approach disclosed in this document provides the best of both of the above, while avoiding their drawbacks.
The physical layer of the Ad-hoc Mesh Tier (AMT) is based on existing WLAN standards, such as the IEEE 802.11 standard, or a variant thereof. This technology is not sufficient enough to handle all the cases in the outdoor environment. Improvements are therefore mandatory. The added features will among others aid in extending the range and improving the interference and error resilience, thereby increasing the system capacity.
Since the physical layer of the AMT has similar RF (radio frequency) characteristics as WLAN, interoperability can be achieved purely by additional software and is therefor not excluded. For example, if the device also has an indoor antenna, it could additionally serve as WLAN base-station on a time-sharing basis.
Comparing the proposed solution with WLAN on the link/network layer level, the proposed solution is superior in that it does not use the concept of base-stations (master/slave approach), which results in higher flexibility and failure resistance. Also, it avoids the thorough network planning required for WLAN networks with multiple base-stations. This is achieved by inband trunking and real-time adaptive network configuration. The link layer protocols will also decrease the systems self-interference.
The proposed solution also implicitly handles the hidden terminal problem, whereas this poses significant scheduling problems in the WLAN approach.
The AMT solution is optimized for both mobile and fixed terminals, where in the system design, special consideration is being given to mobile battery-life.
Compared to a classical PMP (pre-configured Mesh Tier) topology, a Pre-configured Mesh Tier, proposed below, has a higher reliability due to the possibility to connect a node to multiple others, and indirectly to multiple sink-nodes.
Another advantage of the PMT solution, is that not all nodes need to fulfill the LOS or near-LOS (line of sight) requirement to the sink-node, as LOS or near-LOS to any other node which achieves, directly or indirectly, LOS or near-LOS to the sink is sufficient. Hence the PMT solution relaxes the stringent PMP requirements on base-station placement.